HYDROCARBON - Lecture Notes

Brilliant STUDY CENTRE CHEMISTRY -2023 HYDROCARBON Organic compounds which contains both Carbon and Hydrogen. Classification On the basis of carbon skelton, hydrocarbon are mainly two type I. Acyclic / open chain compound II. Cyclic / closed chain compounds I. Acyclic / open chain compounds Compounds contain open chains of carbon atoms in their molecules. They may be either straight or branched. Open chain compounds are also called aliphatic compounds Aliphatic compounds are two types i. saturated hydrocarbon: compounds containing C  C . Also known as alkanes / paraffins ii. unsaturated a. Alkenes / olefins compounds containing C  C b. Alkynes / Acetylenes compounds containing C  C II. Cyclic / closed chain compounds Compounds containing closed chains / rings of carbon atoms. Mainly two types 1) Homocyclic 2) Hetero cyclic 1

Brilliant STUDY CENTRE CHEMISTRY -2023 1. Homocyclic Rings are made up of only one kind of atom, mainly carbon atom so known as carbocy- clic compounds; further divided in to a) Alicyclic compounds Rings are made up of 3 or more carbon atoms and properties resembles with aliphatic compounds Eg. Cyclobutane Cyclopropane b) Aromatic compounds From the word Aroma (Fragnent smell) Two types i) Benzenoid compound Compounds containing one or more fused or isolated benzene rings. OH CH3 Benzene Phenol Toluene Isolated Fused Naphthalene Biphenyl Anthracene Terphenyl ii) Non Benzenoid aromatic compounds 2

Brilliant STUDY CENTRE CHEMISTRY -2023 Compounds does not contains benzene ring but contain other highly unsaturated rings. 2. Heterocyclic compounds Rings contains carbon and hetero atoms a) Alicyclic heterocyclic Alicyclic compounds contains hetero atoms b) Aromatic hetero cyclic Aromatic compounds containing heteroatoms 3

Brilliant STUDY CENTRE CHEMISTRY -2023 Hydrocarbon Acyclic Cyclic Saturated Unsaturated Homocyclic Heterocyclic Alkene Alkyne Aromatic Alicyclic Aromatic Alicyclic Benzenoid Nonbenzenoid Fused Isolated Alicyclic Aromatic I. Alkanes / Paraffins General formula CnH2n2 Preparation 1) From unsaturated hydrocarbon Alkanes are obtained by hydrogenation of unsaturated hydrocarbons (alkenes / alkynes) in presence of catalyst. CH2  CH2 H2  CH 3  CH3 N: 200300C Reaction known as sabatier & senderen reaction CH2  CH2  H2 pt/pd  CH 3  CH3 Room Temp CH  CH  H2 NiCH2  CH2  H2 NiCH3  CH3 4

Brilliant STUDY CENTRE CHEMISTRY -2023 CH2  CH2  H2 RaneyNi  CH3  CH3 Room Temp 2) From alkyl halide a) Using Grignard reagent (R–Mg–x) R  Mg  X  First organometallic compound prepared by victor Grignard using R–X heated with Mg in present of dry ether. R  X  Mg dryether R  Mg  X  8 8 8 is a source of carbanion so react with any H+ medium to form Hydrocar- R  Mg X bon R  Mg  X H2OR  H  Mg OH X CH3MgCl H2O CH4  Mg OH Cl b) Wurtz reaction An ether solution of alkylhalide is treated with sodium form hydrocarbon R  X  2Na  X  R dryether R  R  2NaX This reaction is not suitable for the synthesis of alkane containing odd number of car- bon atoms but the method is useful for the preparation of symmetrical alkanes CH3  Br  2Na  C2H5  Br dryether CH3  CH3  CH3  CH2  CH3  CH3  CH2  CH2  CH3  2NaBr Mixture of product, seperation not easy Mechanism Ionic : 2Na  2Na  2e 2e  R  X  RNa  NaX 5

Brilliant STUDY CENTRE CHEMISTRY -2023 R Na R XR R  NaX Free radical : 2R  X  2Na  2R  2NaX 2 R  R  R Limitation : 1) Methane cannot be obtained 2) Tert alkylhalide does not give the reaction 3) Only for the preparation of symmetrical alkanes. c) Frankland’s reaction Alkylhalide heated with Zn in presence of ether 2R  X  Zn ether R  R  ZnX2 d) Corey-House synthesis Halo alkane react with Li form alkyl lithium R  X  2 Li R  Li  LiX Alkyl lithium react with cuprous iodide form Lithium dialkylcuprate 2R  Li  CuI  R 2CuLi  Li I R2CuLi react with R–X form hydrocarbon. Gilman’s reagent R2CuLi  R ' X  R  R ' R  Cu  LiX CH3  Cl  2Li  CH3  Li  LiCl 2CH3  Li  CuI CH3 2  CuLi  LiI CH3 2  CuLi  CH3  Cl CH3  CH3 CH3Cu  LiCl symmetrical CH3 2  CuLi  CH3  CH2  Cl  CH3  CH2  CH3 CH3Cu  LiCl unsymmetrical 6

Brilliant STUDY CENTRE CHEMISTRY -2023 e) Reduction of alkyl halide Haloalkane react with metals dissolving in acid / base / alcohol R  X ZnHCl R  H R  X ZnNaOH R  H R  X ZnROH R  H Haloalkane reduce with strong reducing agent LiAlH4, R  H is formed R  X LiAlH4 R  H  X 3) From carboxylic acid a) using sodalime Sodium salt of carboxylic acid decarboxylated with sodalime  NaOH  CaO , hydro- carbons having, one carbon less than parent acid is formed. R  COONa  NaOH CaO R  H  Na 2CO3  CH3  COONa  NaOH CaO CH 4  Na 2CO3  b) Kolbe’s electrolytic decarboxylation Aqueous sodium / potassium salt of mono carboxylic acid electrolysis, hydrocarbons are formed having twice the number of carbon atom in the parent alkyl group 2 R  COONa  2R  COO  2Na 2H2O  2OH  2H At Anode 2 R  COO  2R  COO  2e -2CO2 RR 7

Brilliant STUDY CENTRE CHEMISTRY -2023 At Cathode 2H  2e  H2 Eg. 2CH3COONA Electrolysis CH3  CH3 2CH3CH2COONa ElectrolysisCH3 CH2 CH2 CH3 4) Reduction of carbonyl compounds a) Clemmensen reduction Aldehyde and ketones reduced with amalgamated Zn and conc:HCl alkanes are formed C  O ZnHg  CH2 conc.HCl b) Wolf-Kishner reduction Aldehydes and ketones reduced to hydrocarbon in presence of excess hydrazine and sodium alkoxide on heating C  O NH2NH2  C  N  NH2 C2H5ONa CH2 c) Mozingo method C  O is converted into its dithioacetal or ketol using ethanedithiol in presence of Lewis acid. Dithioacetal hydrogenated Chemical reactions get hydrocarbon in presence of Raney Ni HS CH2 S CH2 HS CH2 O+ S Raney CH2 C Lewis C CH2 + HS Ni acid CH2 CH2 HS 8

Brilliant STUDY CENTRE CHEMISTRY -2023 5) By action of water on Be / Al carbide Be2C  4H2O  CH4  2Be OH2 Al4C3 12H2O 3CH4  4AlOH3 Properties 1) Physical properties 1st four members - colourless, odourless, gases C1C4  Next 13 - colourless, odourless, liquids C5 C17  From C - colourless, odourless, solids 17 • Boiling points : Bp of n - alkanes increases regularly with increasing number of carbon atoms. In case of isomeric alkanes branching increases bp • Melting points Chemical Reactions I. Substitution reaction Replacement of H by another atoms / group i) Halogenation Replacement of H by halogen C  H  X2 light  C  X  HX  520 670 K( x = Cl, Br) Halogenation reaction depends on nature halogen and type of H F2  Cl2  Br2  I2 1H  2H  3H CH 4  Cl2 light CH3  Cl  HCl  9

Brilliant STUDY CENTRE CHEMISTRY -2023 Mechanism Initiation :   Cl2 2Cl    Propagation : CH4  C l C H3  H Cl  C H3  Cl2  CH3  Cl  C l  Termination : 2C l Cl2  2 C H3 CH3  CH3  C H3  C l  CH3  Cl In presence of excess Cl all hydrogens are replaced by Cl, 2 CH4  Cl2 light  CH3  Cl  Cl2  CH2Cl2 Cl2 CHCl3 Cl2 CCl4  HCl HCl HCl HCl The relative reactivity of 1, 2 and 3 H towards Cl in the ratio 1 : 2 : 3  1: 3.8 : 5 2 Towards bromination in the ratio 1 : 82 : 1600 The % yield of chlorination or bromination = Re lative amount 100 Total amount CH3  CH2  CH3  Cl2 hu CH3  CH2  CH2  Cl  CH3  CH  CH3 1.  I I Cl II No. of 1°H = 6 Relative amount  61  6 %  6 100  44% 13.6 II No. of 2°H = 2 R.A  2  3.8  7.6 %  7.6 100  56% 13.6 10

Brilliant STUDY CENTRE CHEMISTRY -2023 CH3 CH3 CH3 2. CH3  CH  CH3  Br2 light CH3  CH  CH2  Br  CH3  C  CH3  Br I II I. No. of 1°H = 9 R.A  9 1  9 % yield  9 100  0.6% II. No of 3°H=1 1609 R.A  11600  1600 % yield  1600 100  99.4% 1609 CH3 CH3 CH3 3. CH3  CH  CH2  CH3  Cl2 light  CH3  CH  CH2  CH2  Cl  CH3  CH  CH  CH3  (1) Cl (2) CH3 CH2 Cl CH3  CH  CH2  CH3  CH3  CH  CH2  CH3 Cl (3) (4) 1) No. of 1°H = 3 R.A  31  3 %yield  3 100  14% 21.6 2) No. of 2°H = 2 R.A  2  3.8  7.6 %yield  7.6 100  35% 3) No. of 3° H = 1 21.6 R.A  1 5  5 % yield  5 100  23% 21.6 4) No. of 1°H = 6 11

Brilliant STUDY CENTRE CHEMISTRY -2023 R.A  1 6  6 % yield  6 100  28% 21.6 ii) Nitration H atom replaced by nitro group R  H  HONO2 High  R  NO2  H2O Temp Mechanism HO  NO2  H  N O2 O  R  H  O H  R H2O  R  N O2  R  NO2 Alkanes contain 6 or more carbon atom heating with fuming nitric acid yield nitroalkane C6H13  H  HONO2  C6H13  NO2  H2O  Mixture of vapour of an alkane and nitric acid is heated at 400° – 500°C nitro alkane is formed. This method is known as vapour phase nitration. CH3  H  HONO2 450C CH3  NO2  H2O In alkane having 2 or more carbon atom, there is possibility of C-C bond breakage NO2 C3H8 HNO3 CH3CH2CH2  NO2  CH3  CH  CH3  CH3NO2  CH3CH 2 NO2 450C iii) Sulphonation H atom replaced by SO3H group Higher alkanes contains six or more carbon atom heated with fuming H2SO4 at about 400°C R  H  SO3 H2SO4 R  SO3H  H2O 12

Brilliant STUDY CENTRE CHEMISTRY -2023  HO  SO3H  H O S O3H .   R  SO3H R SO3H R  H   H  R  H2O O II. Oxidation reaction a) Complete oxidation / combustion reaction CnH 2n  2   3n  1  O2  n CO2 n 1 H2O  2  Eg. : CH4  2O2  CO2  2H2O C4H10  13 O2  4CO2  5H2O 2 b) Incomplete oxidation In presence of limited supply of air / oxygen, alkanes give CO along with some unburnt carbon (soot) in the form of carbon black. 2CH4  3O2  2CO  4H2O CH4  O2  C 2H2O  Carbon black / soot Carbon black is used for the preparation of black ink, paint etc. When methane is react with superheated steam in presence of Ni at high temp, water gas is formed CH 4  H2Og Ni  CO  3H 2 1273 K Reaction reversible c) Catalytic oxidation Different catalyst give different product 2CH 4  O2 cu tube CH 3OH  CH 4  O2 MO2O3  HCHO  H2O  13

Brilliant STUDY CENTRE CHEMISTRY -2023 2 R  CH3  3O2 Ag2O  2 R COOH  2H2O  Alkanes having 3°H are oxidise by oxidising agents to corresponding alcohol. CH3 CH3 CH3  CH KCMAnIOK4 CH3  C  OH CH3 CH3 III. Isomerisation Alkanes when heated in presence of an : AlCl and HCl at about 200°C and 35 atm 3 CH3 CH3  CH2  CH2  CH3 An:AlCl3 CH3  CH  CH3 HCl.200C IV. Aromatisation Alkanes contain 6 - 10 carbon atom are heated with metalic oxides and followed by dehydrogenation to form aromatic compounds CH3  (CH2 ) 4CH3 Cr2O3Al2O3  V2O5, 773 K 3H2 CH3 CH3 CH3  (CH2 ) 5CH3 Cr2O3Al2O3  V2O5, 773 K 3H2 CH3  (CH2 ) 6CH3 Cr2O3Al2O3 CH3 CH3 CH3 V2O5, 773 K CH3  x ylene 3H2 V. Pyrolysis Decomposition of a compound by applying heat is known as pyrolysis 14

Brilliant STUDY CENTRE CHEMISTRY -2023 Pyrolysis of alkane to lower members is known as thermal cracking C6H12  H2 C6H14 773- C4H8  C2H6 973 K CH4  C2H4  C3H6 Isomerism in alkanes Conformational isomerism The infinite no. of spatial arrangements obtained due to the rotation around a C-C single bond is known as conformers. The phenomenon is known as conformational isomer- ism • It aries due to the free rotation around a C-C • The energy of arrangement is max when bond pairs are very close to each other, such forms are called eclipsed conformation (Least stable) • The energy of arrangement is min when bond pairs are far a part, such forms are called staggered conformation (more stable) • Conformations between eclipsed and staggered is known as skew conformation aa a cb CC CC b cb c Eclipsed b ca Staggered Conformations of ethane 2) New - man projeciton CH3  CH3 1) Saw - House projection 15

Brilliant STUDY CENTRE H CHEMISTRY -2023 Eclipsed H H H HH H HH HH H H dihedral angle H = 60° H HH H staggered H H HH H Energy level diagram Conformations of butane CH3  CH2  CH2  CH3 16

Brilliant STUDY CENTRE CHEMISTRY -2023 CH3 CH3 CHH3 H CH3 CH3 HH H H H H H H H H Staggered gauche CH3 Fully eclipsed Partially eclipsed CH3 CH3 CH3 HH H3C H H HH HH H3C H H CH3 H H Staggered gauche Anti staggered Partially eclipsed Energy level diagram Alkene General formula CnH2n Isomerism in alkene Geometrical isomerism Two compounds having same molecular formula but different spatial arrangement around a carbon - carbon double bond. Such isomers are called geometrical isomers and the phenomenon is known as geometrical isomerism. 17

Brilliant STUDY CENTRE CHEMISTRY -2023 • If the identical atoms or groups are on same side of C  C is called cis isomer and they are on opposite side trans isomers Eg. But - 2 - ene H3C CH3 H CH3 CC CC H3C H HH Trans Cis Conditions : • Should contain at least 1 double bond • No identical atoms or group are on same carbon atom Preparation I. From alkynes Alkynes undergo partial reduction to form alkenes, Alkynes reduced with H2 in presence of Pd over CaCO3 or BaSO4 with added lead acetate and quinoline - is known as Lindlar catalyst R  C  C  R H2Pd  HH CC BaSO4, CaCO3 Sulpher or Quinoline HR Alkynes on reduced with Li or Na in NH3 give trans alkene: Birch reduction RH R  C  C  R Na  C  C Liq.NH3 HR H2Pd Ph Ph Cis BaSO4, CaCO3 CC HH Ph C  CPh Na Ph H Trans Liq.NH3 CC 18 H Ph

Brilliant STUDY CENTRE CHEMISTRY -2023 II From monohydric alcohols Alcohols undergo dehydration in presence of protonic acid (conc. H2SO4/Conc : H3PO4) or heated with catalyst such as alumina or an. ZnCl give alkenes 2  Conc:H2SO4 C = C +H2O CC  H OH  - Elimination Mechanism CH3 CH2  OH ProtHonationCH3  CH2  DehyHd2raOtionCH3  OH2 CH2 H Deprotonation CH2  CH2 Order of dehydration 3  2  1 CH3CH2  OH H CH 4  CH 2  H2O 443 K CH3 CH3  CH  OH H CH3  CH  CH 2  H2O 440 K CH3 CH3 CH3  C  OH H CH3  C  CH 2  H2O 358 K CH3 CH3  CH2  CH2  CH2  OH H CH3  CH2  CH2   H2  C H2O H shift  CH3  CH2   H  CH3 C 19

Brilliant STUDY CENTRE CHEMISTRY -2023  CH3  CH2  C H  CH3 CH3  CH  CH  CH3 CH3  CH2  CH  CH2 Major Minor In this case more than one product is formed, major product is determind by saytzeff’s rule ie more substituted alkenes are the major product. III. From alkylhalide R-x heated with strong bases such as sodiumethoxide, alc. KOH, tert -butoxide dehydrohalogenation to form alkenes H alc.KOH CC  Hx   CC  x Also known -Elimination The leaving nature of halogens F  Cl  Br  I order of reactivity of R - x 3  2  1 Reaction follows E2 Mechanism. CH3  CH2  CH 2CH 2  Br alc.KOH CH3  CH2  CH  CH2  HBr  In case of terminal halide, terminal alkenes are formed Br CH3  CH2  CH  CH3 alc.KOH CH3  CH  CH  CH3  CH3  CH2  CH  CH2  Maj Min In case of non terminal halides major product is determind by saytzeff rule. If the elimination carried out in presence of a bulky bases Hoffmann’s elimination fol- lows 20

Brilliant STUDY CENTRE CHEMISTRY -2023 Br CH3  CH2  CH  CH3 CH33CO CH3  CH  CH  CH3  CH3  CH2  CH  CH2 Maj E2 elimination depends on periplanar geometry two types of periplanar 1. Syn periplanar - Both H and halogen are on same side x Hx H 2) Anti periplanar - Both H and halogen are on opposite side HH x x E2eliminations are always antiperiplanar CH3 CH3 C l  alc.KOH  N o rea ctio n  CH3 CH3 ++ Ph Ph B r alc.KOH  Ph  M aj ph 4) From vicinal dihalides CH2 x  Z n  eth er  CH2 +ZnX2 CH2 x CH2  21

Brilliant STUDY CENTRE CHEMISTRY -2023 5) From saturated dicarboxylic acids Aqueous solution of sodium / pottasium salt of succinic acid undergo Kolbe’s electro- lytic decarboxylation to form alkene CH2 COOH CH2 COONa 2NaOH  +2H2O CH2 COOH CH2 COONa succinic acid CH2 COONa CH2 COO CH2 COONa  +2Na COO CH2 2H2O  2OH  2H At cathode At Anode CH2 COO CH2 COO CH2 COO  +2e 2H  2e  H2 CH2 COO -2CO2 CH2 = CH2 6) Pyrolysis of ester O CH3  C  O  CH2  CH3  CH 2  CH2  CH3COOH  Mechanism 22

Brilliant STUDY CENTRE CHEMISTRY -2023 Pyrolysis of esters are syn elimination reaction 7) Pyrolysis of Quaternary ammonium salts When quaternary ammonium salts are heated in presence of a base alkenes are formed. CH3 CH3 N  OH CH3   CH2  CH2   C H 2  CH2  N  CH3 CH3 H CH3 Properties Physical properties 23

Brilliant STUDY CENTRE CHEMISTRY -2023 First 3 members are gases Next 14 members are liquids Others are solids Melting and Boiling points Molecular mass increases mp and bp increases Cis isomer having more bp than trans due to more polar nature Trans isomer having higher mp than cis due to more symmetry. Stability Stability of alkenes  No of alpha H atom  Heat of 1 Hydrogenation Heat of Hydrogenation - The amount of energy release when an alkene is hydroge- nated to form alkene 24

Brilliant STUDY CENTRE CHEMISTRY -2023 > >H3C CH3 C=C H3C CH3 H3C H > C=C C=C H3C CH3 H3C H H3C H 12H 9H 6H > >H CH3 C=C H3C CH3 H3C H > C=C C=C H3C H HH HH 6H 6H 3H CH2  CH2 NoH CHEMICAL REACTIONS The  electrons in alkenes are loosely held and easily polarisable in presence of a polar solvent at low temperature heterolytic clevage take place and favour ionic mecha- nism. In presence of a non polar solvents at high tempetrature homolytic clevage takes place and favour free radical mechanism C C nonpolar C  C polar solvent C C high temp low temp homolytic hetrolytic IONIC MECHANISM Alkenes show electrophilic addition reaction through 3 steps E  Nu ionise E  N u Generation of electrohile 25

Brilliant STUDY CENTRE CHEMISTRY -2023 SE Formation of carbocation C  C  E   C  C E E Nu formation of addition product C  C  Nu  C  C IMPRORTANT ADDITION REACTION 1) Addition of Hydrogen CH 2  CH2 H2 CH3  CH3 N1 2) Addition of hydrogen halide C  C  HX Dark  C  C  Formation of alky halide HX Mechanism HX  H  X C  C  H  C  CH x  C  C  XH HH C  C  A B r   C H 3  C H 2  B r HH Ethyl bromide CH3  CH  CH2  HCl Dark CH3  CH2  CH2  Cl  CH3  CH  CH3 Cl (Major) 26

Brilliant STUDY CENTRE CHEMISTRY -2023 In this reaction morethan one product is formed therefore reaction is a regioselective reaction so the major product is determined by using “Marconicoff rule” The rule states that addition of unsymmetrical reagent to an unsymmetrical alkene the negative part of the adding molecule attached to the carbon containing lesser number of H-atom Proof for Markovnikov rule: CH3  CH  CH2  H+ more stable   CH3  C H  CH2 2 C   CH3  C H  C H2 1 C 2°C is more stable hence it forms the major one. This reaction occurs due to electromeric shift. The reason for the repulsion of electrons to the next is due to +I effect of methyl thus providing a pushing force. • Addition of HBe [not HF, HCl and HI] to an unsymmetrical alkene in presence of perox- ide addition takes place against to Marconicoff rule known as Anti Marconicoff’s Addi- tion/ Peroxine Effect / Kharasch Effect. CH3  CH  CH2  HBr Peroxide CH3  CH2  CH2  HBr  CH3  CH  CH3 Benxoyl Peroxide Major Initiation OO O C6H5  C  O  C  C6H5  2C6H5  C  O Benzoyl free radical O C6H5  C  O  C6 H5  CO2 C6 H5  HBr  C6H5  B r Propagation CH3  CH  CH2  Br CH3  27

Brilliant STUDY CENTRE CHEMISTRY -2023 CH3  CH  CH2  Be  HBr  CH3  CH2  CH2  Be  Br Termination 2B r  Br2 CH3  C H  CH2  Br  B r CH3  CH  CH2 Br Br CH3  C H  CH2  Br CH3  CH  CH2  Br +  CH3  CH  CH2  Br CH3  C H  CH2  Br (1) (2)  Exothermic process stable HF  + HCl  + HBr   HI +  3) Addition of H O 2 1. Acidic Hydration of Alkane C  C H/H2O  C  C  H OH CH2  CH2 H/ H2O CH3  CH2OH CH3  CH  CH2 H/ H2O CH3  CH2OH CH3  CH  CH3 OH 28

Brilliant STUDY CENTRE CHEMISTRY -2023 CH3 CH3 CH3  C  CH2 H/ H2O CH3  C  CH3 OH Alcohols are Marconicoffs alcohol H2 O  H  H3O  HH C  C  H  O protonation  C   H   H  C O  H HH C  C H    H hydration C  C  O  O HH H  C  C  dehydration HC  CH  H O HH 3, 3 dimethyl but -1- ene + dilute H2SO4 CH3 CH3 CH2  CH  CH  CH3  CH3  CH  CH  CH3 CH3 CH3 CH3 CH3 CH3  CH3  C H CH  CH3  H  O  H CH3  C  CH  CH3 CH3 OH 29

Brilliant STUDY CENTRE CHEMISTRY -2023 2. Hydroboration - Oxidation When alkenes react with borane form trialkyl borane which on oxidised with H2O2in alkeline medium alchohols are formed Anti Marconicoff’s alchohol. B2H6  2BH3 CH3  CH  CH2 HBH2 CH3  CH2  CH2  BH2 CH3-CH2=CH2  3CH3  CH2  CH 2  OH alkali CH3  CH2  CH2  B CH3CH2 CH2  CH3  CH2  CH2 2  BH  H2O2 H2O2 H3BO3 Syn addition CH3  CH  CH2 H BH2 HBO H CH3 OH H H OH OH 3. OXYMERCURATION - DEMERCURATION It is hydration of an alkene to form Marconicoff’s alchohol, there is no intermediate form- ing. HgOAC 2 /H2O redagent CH3  CH  CH 2 NaBH 4 CH3  CH  CH  H OH 30

Brilliant STUDY CENTRE CHEMISTRY -2023 ACO  Hg  OAC  CH3  CH  CH2  Hg OAC CAO  Hg  OAC  Hg OAC CH3  CH  CH2  H2O  CH3  CH  CH3  HgOAC  CH3  C  CH2  Hg OAC OH O HH CH3  CH  CH3 O H CH3  CH  CH 2 HgOAC2 /H2O CH3  CH  CH2  D NaBD4 OH CH3  CH  CH2 HgOAC 2 / D2O CH3  CH  CH2  H NaBH4 OD 4. ALKOXY MERCURATION - DEMERCURATION OR CH3  CH  CH2 HgOAC2 /ROH CH3  CH  CH3 NaBH4 OH DMDM OH HBO 31

Brilliant STUDY CENTRE H CHEMISTRY -2023 H  OH H2O ADDITION OF HALOGEN Formation of vianal halide X C  C  X2 CCl4C  C  X X C  C  X  X  C  C X C  C X X These are antiaddition so forming vicinal dihalides CH2  CH2  Br2 CCl4CH2  CH2 Br Br The reddish brown colour of bromine is discharged and colourless vicinal debromide is formed, this reaction is used for test for unsaturation. CH3 CH3 Br CH3 H CH3 C  C  Br2 CCl4  H H Br Br Antiaddition H CH3 Br CH3 H H (CAR) cis Racemic Mixture 32

Brilliant STUDY CENTRE CHEMISTRY -2023 H CH3 Br CH3 CC Br H  Br2 CCl4 H CH3 Antiaddition CH3 Meso H Br 1, 2 addition Br2 CCl4  Br Br Br 1, 4 addition Br 40°C Br If alkenes containing nucleophilic center cyclisation takes place Br OH Br2  O + HBr 33

Brilliant STUDY CENTRE CHEMISTRY -2023 .. B .. O H O H Br2  Br Br OH O HBr ADDITION OF CARBENE Formation of cycloalkane CH2  CH2  : CH 2 hv CH2  CH2  CH2 CH 2 N 2 hv : CH 2  N2  CH2  C  O hv : CH 2  CO Ketene  CHCl3 OH  CCl2 Cl  : CCl2 H2O CH3  CH  CH 2  CHCl3  CH3  CH  CH2 CCl2 1, 1 dichloro 2 methyl cyclopropane ADDITION OF HYPOHALOUS ACID Formation of halohydrin X2  H2O  OH  X  HX  hypohalous acid 34

Brilliant STUDY CENTRE CHEMISTRY -2023 OH CH2  CH2  X2 H2O CH2  CH2 X H CH2  CH2  XX CH2 CH2 H2OCH2 CH2 O X H X OH HXCH2 CH2 X Cl CH3  CH  CH2  Cl2 H2O CH3  CH  CH2 OH ALKENES SUBSTITUTION REACTION Higher alkenes are heated with halogen under higher emperature, H atoms from alkyl / benzylic carbon replaced halogenation taking place and this halogenation is known as Alkylic / benzylic halogenation CH 2  CH  CH3  X2  CH 2  CH  CH 2Cl 500C  CH2  CH  C H2  C H2  CH  CH2 CH3 CH2-X + X2  +HX 35

Brilliant STUDY CENTRE CHEMISTRY -2023  CH2 Allyl and benzyl radicals are resonance stabilised. CH 2  CH2  X2  not possible 500C O CH2  CH  CH3  NBS  CH  CH  CH2Cl  NH 425 K 2 O O Br N - Bromo Succinamide NBS  CH2  C N CH2  C O OXIDATION REACTION 1. Complete oxidation CnH2n  3n O2  nCO2  nH2O 2 Eg. C2H4  3O2  2CO2  2H2O 2. Incomplete / partial oxidation CH2  CH 2  1 O2 Ag2 CH2  CH2 Epoxide 2 O Epoxide undergo acidic hydrolisis give vicinal diol and reaction is known as hydroxyla- tion 36

Brilliant STUDY CENTRE CHEMISTRY -2023 OH CH2  CH2 H/H2O CH2  CH2 O OH HH OH O CH2  CH2 H CH2  CH2  CH2CH2 H2O CH2  CH2  CH2  CH2 O OH OH OH OH Anti hydroxylation CH3  CH  CH2 H /H2O CH3  CH  CH2  OO H OH CH3  +  CH2 H2 O  CH3  CH  CH2 CH OH OH O CH2  CH2 RCOOH CH2  CH2  RCOOH Peroxy acid/peracid O CH2  CH2 KOMHnO2O4 CH2  CH2 O CH3  CH  CH2 CH3 COOH CH3  CH  CH2  CH3COOH peroxy acetic acid O 37

Brilliant STUDY CENTRE CHEMISTRY -2023 COOH CH 2  CH2  M  CPBA  CH 2  CH 2  Cl O O COOH Meta chloro peroxy benzoid acid = Cl MCPBA O H/H2O OH OH Oxidation using DIWTE/cold KMnO4 2KMnO4  2KOH  2MnO2  3O  nascent oxygen CH2  CH2 OKMHnO2O4 CH2  CH2 OH OH syn addition vicinel diol The purple colour / KMnO is discharged and colourless, Vicinal diol is formed is known 4 as Baeyer’s test for unsaturation CH3 CH3 CH3 C  C dil.KMnO4  H OH syn addition H OH HH CH3 38

Brilliant STUDY CENTRE CHEMISTRY -2023 H CH3 CH3 CH3 H OH OH H dil. KMnO4  CC CH3 H OH HH OH CH3 CH3 Oxidation using Acidified or Alkaline hot KMnO4/K2Cr2O7 CH2  CH2  2CO2  2H2O CH3  CH2  CH2  CH3  COOH  CO2  H2O Terminal can be converted into CO2 and H2O CH3  CH  CH  CH3  2CH3  COOH Without terminal the respective acids will be formed CH3  CH2  CH  CH  CH3  CH3  CH2  COOH  CH3  COOH If no H is present on C then ultimately it becomes CO(Keto) CH3 CH3 CH3  C  CH  CH3  CH3  C  O  CH3COOH KMnO4  HOOC  CH 2 4 COOH O, H adipic acid Oxidation using OSO4 CH2 OO CH2 OO CH2 OH + OS  CH2 OH OS alc CH2 OO OO CH2 Syn hydroxylation 39

Brilliant STUDY CENTRE CHEMISTRY -2023 H2O2 OH HCOOH OH dil. KMnO4 syn epoxide + H+ H2O2 + HCOOH anti hydroxylation OSO4 hydroxylation OZONOLYSIS REACTION C  C  O3  C O H2O2 /AgO Oxidative ozonolysis O C Ozonide O Zn H2O /Me2S Reductive Ozonolysis O ozonolysis CH2  CH2  O3 ZnH2O CH2 CH2 ZnO 2H  C  H O OO O CH3 CH  CH2 O3 ZnH2OCH3 C CH2 ZnOCH3CHOHCHO O O O CH CH3  2CH3CHO CH3  CH  CH  CH3  O3  CH3  CH O O CH3 CH3  C  C  CH3  O3  CH3  COCH3  CH3CHO 40

Brilliant STUDY CENTRE CHEMISTRY -2023 OO CH3  C  H  CH3  C  H  CH3  CH  CH  CH3 CH3  CH  O  O CH2 CH3  CH  CH2 Oxidate ozonolysis O CH3 Zn.H2O CH3  CH2  CHO  CH3CHO CH3  CH2  CH CH2 (for oxidation just add o) OO H2O2AgS CH3  CH2  COOH  CH3  COOH POLYMERISATION REACTION Conversion of monomer  polymer • At 473 k and 1500 atm n CH2  CH2  ( CH2  CH2 ) n ethene polythene CH3 n CH2  CH  CH2  ( CH2  CH2 ) n propyne polypropyne Cl n CH2  CH  Cl  n ( CH2  CH2 ) polyvinyl chloride (pvc) 41

Brilliant STUDY CENTRE CHEMISTRY -2023 n CH2CH  n ( CH2  CH2 ) ph ph Styrene Polystyrene n CH2  CH  ( CH2  CH ) n CN CN Acrylnitrile Polyacrylonitrile (PAN) CF2  CF2  ( CF2  CF2 ) n CH3 CH3 n CH2  C  CH  CH2 TEFLON ( CH2  C  CH  CH2 ) n Isoprene Polyisoprene DIMERISATION CH3 2CH3  C  CH  CH2 H2SO4 CH3 3  C  CH2  C  CH3 2 CH3 CH3 CH3  C  CH2  C  CH3  CH3  C  CH2  C  CH3 CH3 CH3 CH3 CH3 CH3 3  C  CH2  C ( CH3)2 Diels Alder Reaction (4 + 2) Cycloaddition of conjugated alkene with an enophile  /  42

Brilliant STUDY CENTRE CHEMISTRY -2023 +  O O O + O  OO ALKYNES • General formula : CnH2n2 • Less than 4 H atom corresponding paraffins • Known as acetylene • First member is acetylene others are derivatives of acetylene Eg. CH  CH methylene CH3  C  C  CH3 CH3  C  C  CH2  CH3 CH3  C  CH3 Dimethyl acetylene Methyl acetylene CH2  CH  C  C  CH2  CH  CH2 180° H  C C H   Alkyl vinyl acetylene   sp 121 pm 106 pm The four half filled orbitals on each C atom merge together to form a single electron cloud in a cylindrical cloud. The C - H bond is passing through the center of the cylinder its bond angle always remains 180° and linear geometry. 43

Brilliant STUDY CENTRE CHEMISTRY -2023 Alkynes are less reactive than alkenes due to 1. the cylindrucal geometry e are not readily available for reactions. 2. Due to the sp hybridised C - atom  i are tightly held by the nucleus thus  i are not readily available. PREPARATION 1. addition of H O on CaC 22 CaC2  H2O  CH  CH  Ca OH2 CaCO3  CaO  CO2  CaO  3C      CaC 2  CO 20003000C 2. from alkyl halide  from dihalide CH2  CH2 alc.KOH CH2  CH2  X alc.KOH CH  CH  HX O XX This product formed CH2  CH2  X is resonance stabilised  CH     CH 2  CH  X CH2 X  Thus the reaction is very slow hence we can speed up the reaction by using NaNH 2 which is more basic CH 2  CH  X  NaNH2 CH  CH  HX  There two step reaction can be concluded into one step using NaNH 2 44

Brilliant STUDY CENTRE CHEMISTRY -2023 CH2  CH2 2NaNH2 CH  CH  2HX XX From geminal halide X alc.KOH  CH 2  CH  X alc.COH  CH  CH CH3  CH   X CH 3  CHX 2 2NaNH2  CH  CH  HX  From Haloform  2CHX3 6 Ag  CH  CH  6AgX CHX3  6Ag  X3CH  CH2  CH  6AgX 2CHCl3  6Ag  CH  CH  6AgCl Tetrahalide XX CH CH + 2Zn CH CH + 2ZnX  XX 3. From unsaturated dicarboxylic acid COOH COOH COOH H COOH CH C C cis C C trans CH COOH H H COOH H Maleic acid Fumaric acid Aquarous Na/K salt of maleic/fumeric acid undergoes kolbe electrolytic decarboxylation. CH2 COOH 2NaOH CH2 COONa CH2 COOH CH2 COONa 45

Brilliant STUDY CENTRE CHEMISTRY -2023 CH2 COONa CH2 COO- + Na+ CH2 COO- + Na+ CH2 COONa H2O  H  OH CH2 COO At cathode At anode + 2e- 2H  2e  H2 CH2 COO CH2 COO CH2 COO CH CH 4. From C and H Berthlot method Passing H2 gas through an electric arc stuck between carbon electrode 2C  H2 3000C CH  CH 5. Preparation of higher alkynes using acetylenes Acetylene react with metals form metal acetylide. These metal acetyldes reawct with haloalkenes form higher alkynes 2CH  CH  2Na  2CH  C  Na  H2 2CH  C  Na  2R  X SN2 2CH  C  R  2NaX CH  CH  Na  CH3  Cl  CH  CH  CH3  NaCl CH  CH  2NaX  Na  C  C  Na  2HX Na  C  C  Na  2R  X  R  C  C  R  2NaX Na  C  C  Na  2CH3  Cl  CH3  C  C  CH3  2NaCl Physical properties • Acetylene is a colourless odourless gas • First 3 members are gas next 8 members are liquid remaining are solids. MELTING POINT AND BOILING POINT • Melting and boiling points are higher than alkenes due to symmetrical and more polar in nature. • When size or mol mass is high, boiling point melting point will be high Solubility Insoluble in H2O and soluble in organic solvents Chemical reactions 46

Brilliant STUDY CENTRE CHEMISTRY -2023 1. Acidic character of an alkenes 1. Formation of alkalimetal acetalides Thermal alkynes react with alkali metals and forms alkali metal acetalides and there acetalides react with H2O and regenerate acetylene. This shows water is more acidic than acetylene. 2R  C  CH  2Na  2R  C  CNa R  C  CNa  H2O  R  C  CH  NaOH 2. Formation of heavy metal acetylide Acetaline react with Tollens reagent 2Ag  NH3 2  OH ammoniacal silver nitrate from silver acetalide. CH  CH  2 Ag  NH3    OH  Ag  C  C  Ag  4NH3  2H2O 2 ( White ppt ) Acetylene reacted with ammoniacal cuprous chloride. CH  CH  2 Cu  NH3   OH   Cu  C  C  Cu  4NH3  4H2O 2  red ppt There reagents are used for the detection of terminate alkynes to alkenes. Ag  C  C  Ag  2HCl  CH  CH  2AgCL Thus acetylene are weaker than mineral acids 3. Formation of alkynyl grignard reagent CH  CH  R  MgX  CH  C  MgX  RH Reason for acidic In acetylene C is sp  so more s character so highly electronegativity. Thus it withdraws electrons from C–H bonds and thus releases H+ atom. ADDITION REACTION 1. Addition of hydrogen CH  CH  H2 Ni CH2  CH2 OH  196 kj / mol CH2  CH2  H2 Ni CH3  CH3 OH  138 kJ / mol Catalytic hydrogenation of alkynes is more spontaneous then catalytic hydrogenation of alkanes to alkenes. CH3  C  C  CH  CH2 HC2aCOpo3l CH3  CH  CH  CH  CH2 Therefore alkynes are more reactive than alkenes. In hydrogenation alkynes are more stable hence whenever add H to  as to form more stable compounds. 2. Addition of halogen CH CH + X2 CCl4 X X X HC CH X2 CH CH 47 X X X

Brilliant STUDY CENTRE Cl CHEMISTRY -2023 CH CH CH CH + Cl2 CCl4 Cl Cl Cl Cl2 CH CH Cl Cl 1,1,2,2 tetrachloroethene Eg : CH Br Br Br CH + Br CCl4 CH CH Br CH CH Br Br Br Reddish brown Colourless 3. Addition of hydrogen halide X CH CH + HX CH2 CH X + HX CH3 CH X CH2 CH X CH CH2 X CH3 CH X -X This is resonance stabilised CH3 CH X X 48

Brilliant STUDY CENTRE CH2 CH Br HBr CH3 CHEMISTRY -2023 CH CH + HBr CH2 Br Br 1,2,dibromoethane Catalytic hydrogenation of alkynes is more spontaneous then catalytic hydrogenation of alkanes to alkenes. CH3 C C CH CH2 H2-pd CH3 CH CH CH CH2 CaCO3 Therefore alkynes are more reactive than alkenes. In hydrogenation alkynes are more stable hence whenever add H to  as to form more stable compounds. 2. Addition of halogen CH CH + X2 CCl4 X X2 X X HC CH CH CH X X X CH CH + Cl2 CCl4 Cl Cl Cl CH CH Cl2 CH CH Cl Cl Cl 1,1,2,2 tetrachloroethene Eg : CH CH + Br CCl4 Br Br Br Br CH CH CH CH Br Br Reddish brown Br Colourless 3. Addition of hydrogen halide X CH3 CH X CH CH + HX CH2 CH X + HX 49

Brilliant STUDY CENTRE CHEMISTRY -2023 CH2 CH X CH CH2 X CH3 CH X This is resonance stabilised -X CH3 CH X X CH CH + HBr CH2 CH Br HBr CH3 CH2 Br Br 1,1 dibromoethane Br CH3 C CH + 2HBr CH3 C CH3 Br 2, 2 dibromopropane ADDITION OF H2O Due to low reactivity of lakynes it reacts in presence of mercuric ion. O CH CH dil.H2SO4 CH2 COHOH CH3 C H HgSO4 50